The invention relates to a magnetic resonance (MR) method for the imaging of an object arranged in a steady magnetic field, whereas the following steps being repeatedly executed according to said method:    excitation of spins in a part of the object,    slices are selected within the Field-of-View (FOV) of the object to be scanned,    said selected slices are scanned in an oblique relationship with respect to the Cartesian coordinate system of a rectangular area of interest, and    measurement of MR signals along a predetermined trajectory containing a plurality of lines in said slices in k-space by application of a read gradient and other gradients.
The invention also relates to an MR device for carrying out such a method.
It is generally known in multiple slice imaging techniques that parallel slices are imaged in such a manner that if parallel slices are rotated they are kept at the same position to each other in order to obtain a proper image of the object. However, backfolding artifacts cannot always be prevented as parts outside of the rectangular FOV will be covered also by the scan.
In magnetic resonance imaging there is further a general tendency to obtain acceptable images within shorter periods of time. For this reason the sensitivity encoding method called “SENSE” has recently been developed by the Institute of Biomedical Engineering and Medical Informations, University and ETH Zürich, Switzerland. The SENSE method is based on an algorithm which acts directly on the image as detected by the coils of the magnetic resonance apparatus and which subsequent encoding steps can be skipped and hence an acceleration of the signal acquisition for imaging by a factor of about two to three can be obtained. Crucial for the SENSE method is the knowledge of the sensitivity of the coils which are arranged in so called sensitivity maps. In order to accelerate this method there are proposals to use raw sensitivity maps which can be obtained through division by either the “sum-of-squares” of the single coil references or by an optional body coil reference (see e.g. K. Pruessmann et. al. in Proc. ISMRM, 1998, abstracts pp. 579, 799, 803 and 2087). In fact the SENSE method allows for a decrease in scan time by deliberately undersampling k-space, i.e. deliberately selecting a scanning Field-of-View (FOV) that is smaller than the object to be acquired. From this undersampling fold-over artifacts are obtained which can be resolved or unfolded by the use of the knowledge of a set of distinct coils having different coil sensitivity patterns. The undersampling can be in either one of both phase-encoding directions.
If the object exceeds the FOV to be reconstructed (in the phase encoding SENSE direction) residual backfolding will occur with the SENSE method which will be apparent somewhere in the middle of the image.